TW Puddles Counter.js

// https://ramdajs.com/repl/#?%2F%2F%20https%3A%2F%2Fphilipnilsson.github.io%2FBadness10k%2Ffunctional-waterflow%2F%0A%0Aconst%20input%20%3D%20%5B2%2C%205%2C%201%2C%202%2C%203%2C%204%2C%207%2C%207%2C%206%5D%0A%2F%2F%20const%20input%20%3D%20%5B2%2C%201%2C%203%2C%204%2C%201%2C%202%2C%201%2C%203%2C%202%2C%201%2C%200%2C%202%2C%204%2C%203%2C%201%2C%205%2C%203%2C%201%2C%204%2C%201%2C%202%2C%201%2C%200%2C%205%2C%202%2C%201%2C%203%5D%0A%0A%0A%2F%2F%20When%20is%20a%20one%20block%20%60b%60%20of%20%60height%28b%29%60%20filled%20with%20water%3F%0A%0A%2F%2F%20there%20is%20some%20bL%20%28on%20the%20left%29%20that%20has%20height%28bL%29%20%3E%20height%28b%29%0A%2F%2F%20and%20there%20is%20some%20bH%20on%20the%20right%20that%20has%20height%28bH%29%20%3E%20height%28b%29%0A%0Aconst%20mapIndexed%20%3D%20addIndex%28map%29%0A%0A%2F%2F%20For%20each%20index%20in%20the%20input%2C%20compute%20highest%20wall%20from%20the%20left%20side%0Aconst%20leftWalls%20%3D%20source%20%3D%3E%20map%28%0A%20%20i%20%3D%3E%20pipe%28%0A%20%20%20%20take%28i%29%2C%0A%20%20%20%20reduce%28max%2C%200%29%2C%0A%20%20%20%29%28source%29%0A%29%28range%280%2C%20source.length%29%29%0A%0Aconsole.log%28%27left%20walls%3A%27%2C%20leftWalls%28input%29%29%0A%0A%2F%2F%20The%20same%20just%20from%20the%20other%20side%0Aconst%20rightWalls%20%3D%20pipe%28reverse%2C%20leftWalls%2C%20reverse%29%0Aconsole.log%28%27right%20walls%3A%27%2C%20rightWalls%28input%29%29%0A%0Aconst%20data%20%3D%20zip%28input%2C%20zip%28%0A%20%20leftWalls%28input%29%2C%0A%20%20rightWalls%28input%29%0A%29%29%0A%0A%2F%2F%20For%20each%20i%20in%20input%2C%20compute%20how%20much%20of%20water%20it%20will%20keep%0Aconst%20contributions%20%3D%20map%28%28%5Bheight%2C%20%5BleftHeight%2C%20rightHeight%5D%5D%29%20%3D%3E%20%7B%0A%20%20const%20waterKept%20%3D%20min%28leftHeight%2C%20rightHeight%29%20-%20height%0A%20%20return%20max%280%2C%20waterKept%29%0A%7D%29%28data%29%0A%0A%0Asum%28contributions%29%0A%0A

// https://philipnilsson.github.io/Badness10k/functional-waterflow/

const input = [2, 5, 1, 2, 3, 4, 7, 7, 6]
// const input = [2, 1, 3, 4, 1, 2, 1, 3, 2, 1, 0, 2, 4, 3, 1, 5, 3, 1, 4, 1, 2, 1, 0, 5, 2, 1, 3]


// When is a one block `b` of `height(b)` filled with water?

// there is some bL (on the left) that has height(bL) > height(b)
// and there is some bR on the right that has height(bR) > height(b)

const mapIndexed = addIndex(map)

// For each index in the input, compute highest wall from the left side
const leftWalls = source => map(
  i => pipe(
    take(i),
    reduce(max, 0),
   )(source)
)(range(0, source.length))

console.log('left walls:', leftWalls(input))

// The same just from the other side
const rightWalls = pipe(reverse, leftWalls, reverse)
console.log('right walls:', rightWalls(input))

const data = zip(input, zip(
  leftWalls(input),
  rightWalls(input)
))

// For each i in input, compute how much of water it will keep
const contributions = map(([height, [leftHeight, rightHeight]]) => {
  const waterKept = min(leftHeight, rightHeight) - height
  return max(0, waterKept)
})(data)


sum(contributions)